1. Field of the Invention
The present invention relates to a multi-cylinder engine for a vehicle, in which a pair of cylinder bore rows, each including a plurality of cylinder bores disposed in parallel to each other, are disposed in such a manner as to be perpendicular to a crank shaft disposed substantially in the horizontal direction.
2. Description of Related Art
A multi-cylinder engine of this type has been known, for example, from Japanese Patent Laid-open No. Sho 61-291760. This prior art multi-cylinder engine includes a pair of cylinder bore rows disposed in an approximately V-shape. The pair of cylinder bore rows is generally configured such that a single cam shaft is disposed on an extension of the axial lines of cylinder bores or a pair of cam shafts are disposed on both of the sides of the extension of the axial lines of the cylinder bores. Such a disposition of the cam shaft; however, causes a problem in that the valve system mechanisms containing the cam shafts are disposed in spaces on both sides of the extension of the axial lines of the cylinder bores.
On the other hand, in the case where a V-shaped multi-cylinder engine or a horizontally-opposed type multi-cylinder engine is mounted on a motorcycle in such a manner that the axial line of the crank shaft extends in the longitudinal direction, it is required to ensure a relatively large space under a cylinder head for increasing the bank angle of the motorcycle and for ensuring a space allowing the driver""s feet to extend forwardly under the cylinder head. However, the prior art disposition of the cam shaft fails to obtain a multi-cylinder engine capable of satisfying the above requirement.
In view of the foregoing, the present invention has been made, and an object of the present invention is to provide a multi-cylinder engine having a pair of cylinder bore rows, which is capable of ensuring a relatively large space under the cylinder head.
To achieve the above object, according to a first aspect of the present invention, a multi-cylinder engine for a vehicle includes a pair of cylinder bore rows, each including a plurality of cylinder bores disposed in parallel to each other. The cylinder bore rows are disposed in such a manner as to be perpendicular to a crank shaft disposed substantially in the horizontal direction. Furthermore, cam shafts corresponding to the cylinder bore rows are offset upwardly from a pair of planes containing the axial lines of the cylinder bores constituting the cylinder bore rows, respectively.
With this configuration, since the cam shaft corresponding to each cylinder bore row is offset upwardly from the plane containing the axial lines of the cylinder bores constituting the cylinder bore row, the valve system mechanism containing the cam shaft is offset upwardly from the axial lines of the cylinder bores. As a result, it is possible to form the cylinder head in such a manner as to ensure a relatively large space under the cylinder head.
According to a second aspect of the present invention, in addition to the configuration of the first aspect of the present invention, the engine is mounted on the motorcycle in such a manner that the cylinder bore rows are opposed to each other with the axial lines of the cylinder bores extending substantially in the horizontal direction. Furthermore, the crank shaft extends in the longitudinal direction of the motorcycle. With this configuration, when the horizontally-opposed type multi-cylinder engine is mounted on the motorcycle with the cylinder heads protruding from both sides of the motorcycle in the width direction, it is possible to ensure a sufficient space allowing the driver""s feet to extend forwardly under the cylinder heads, and to set the bank angle of the motorcycle at a relatively large value.
According to a third aspect of the present invention, in addition to the configuration of the first aspect of the present invention, the engine is mounted on the motorcycle in such a manner that the cylinder bore rows are disposed in an approximately V-shape. Furthermore, the crank shaft extends in the longitudinal direction of the motorcycle. With this configuration, when the V-shaped multi-cylinder engine having the V-shape opened upwardly is mounted on the motorcycle, it is possible to set the width of the multi-cylinder engine along the width direction of the motorcycle at a relatively small value, and hence make the V-shaped multicylinder engine compact.
According to a fourth aspect of the present invention, in addition to the configuration of the invention described in any of the first through third aspects of the present invention, cams for directly opening/closing intake valves and exhaust valves disposed in cylinder heads for each of the cylinder bores are provided on the cam shafts, respectively. With this configuration, it is possible to simplify the configuration of the valve system mechanism driving the intake valves and exhaust valves.
According to a fifth aspect of the present invention, in addition to the configuration of the fourth aspect of the present invention, the cam shafts common to the intake valves and the exhaust valves are disposed for the cylinder bore rows, respectively. With this configuration, since the cam shaft may be provided for each cylinder bore row, it is possible to make the cylinder head compact.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.